The example appears to be an attempt to make sure that the child recognizes that the carrying is occurring from one register to the next higher one, and to focus the child's attention on the proper place for the carried digit when writing it. The extra horizontal line seems to be an attempt to make sure the child sees the carried digit(s) apart from the original ones.
I can see that the notation would be a bit confusing at first glance. Still, it's nothing your daughter can't handle. I guess it's good that she learn to be able to deal with different types of notation, although I agree with you that simplicity is often best.
ETA: I think it seems suboptimal, but it is hard to portray things with just typography and it might not be as bad as it seems. If the column lines were in light gray, for instance, they'd serve the useful purpose of keeping things lined up (which is something kids tend to have trouble with in my experience) without being so obtrusive and potentially confusing. I definitely think, though, that the line separating the carried digits from the rest is unnecessary, since the little box is there.
